Spring Boot Microservices REST API Example

In this tutorial, we will create two Spring Boot microservices that communicate with each other via REST APIs. This guide is intended for beginners and includes detailed explanations for each step.

Introduction

In a microservices architecture, an application is composed of multiple loosely coupled services that communicate with each other. Each service is responsible for a specific piece of functionality and can be developed, deployed, and scaled independently. REST APIs are a common way for microservices to communicate.

Prerequisites

• JDK 17 or later
• Maven or Gradle
• IDE (IntelliJ IDEA, Eclipse, etc.)

Step 1: Create the Projects

We'll create two Spring Boot projects: product-service and order-service.

Step 2: Set Up product-service

2.1 Create the Project

Use Spring Initializr to create a new project with the following dependencies:

• Spring Web
• Spring Boot Actuator

2.2 Configure application.properties

Set up the application properties for product-service.

server.port=8081
spring.application.name=product-service

Explanation:

• server.port=8081: Sets the port for the Product Service.
• spring.application.name=product-service: Names the application.

2.3 Create a Product Model

Create a simple Product model to represent the product data.

package com.example.productservice;

public class Product {
    private String id;
    private String name;
    private double price;

    // Constructor, getters, and setters
    public Product(String id, String name, double price) {
        this.id = id;
        this.name = name;
        this.price = price;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public double getPrice() {
        return price;
    }
}

Explanation:

• This class represents the product data with attributes id, name, and price.

2.4 Create a Controller

Create a controller to handle product-related requests.

package com.example.productservice;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class ProductController {

    @GetMapping("/products/{id}")
    public Product getProduct(@PathVariable String id) {
        // In a real application, this data would come from a database
        return new Product(id, "Sample Product", 99.99);
    }
}

Explanation:

• @RestController: Marks this class as a REST controller.
• @GetMapping("/products/{id}"): Maps GET requests to /products/{id} to this method.
• @PathVariable String id: Extracts the id from the URL.

Step 3: Set Up order-service

3.1 Create the Project

Use Spring Initializr to create a new project with the following dependencies:

• Spring Web
• Spring Boot Actuator
• OpenFeign (for inter-service communication)

3.2 Configure application.properties

Set up the application properties for order-service.

server.port=8082
spring.application.name=order-service

# URL of the product service
product.service.url=http://localhost:8081

Explanation:

• server.port=8082: Sets the port for the Order Service.
• spring.application.name=order-service: Names the application.
• product.service.url=http://localhost:8081: Specifies the URL of the Product Service.

3.3 Enable Feign Clients

Enable Feign clients by adding the @EnableFeignClients annotation in the main application class.

package com.example.orderservice;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableFeignClients
public class OrderServiceApplication {
    public static void main(String[] args) {
        SpringApplication.run(OrderServiceApplication.class, args);
    }
}

Explanation:

• @EnableFeignClients: Enables Feign client functionality in your Spring Boot application.

3.4 Create a Product Client

Create a Feign client interface to communicate with the product-service.

package com.example.orderservice;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;

@FeignClient(name = "product-service", url = "${product.service.url}")
public interface ProductServiceClient {

    @GetMapping("/products/{id}")
    Product getProductById(@PathVariable String id);
}

Explanation:

• @FeignClient(name = "product-service", url = "${product.service.url}"): Declares this interface as a Feign client for the product-service.
• @GetMapping("/products/{id}"): Maps the GET request to the /products/{id} endpoint in product-service.

3.5 Create a Product Model

Create a Product model to match the one in product-service.

package com.example.orderservice;

public class Product {
    private String id;
    private String name;
    private double price;

    // Constructor, getters, and setters
    public Product() {}

    public Product(String id, String name, double price) {
        this.id = id;
        this.name = name;
        this.price = price;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public double getPrice() {
        return price;
    }
}

Explanation:

• This class represents the product data with attributes id, name, and price.

3.6 Create a Controller

Create a controller to handle order-related requests and use the ProductServiceClient to fetch product details.

package com.example.orderservice;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class OrderController {

    private final ProductServiceClient productServiceClient;

    public OrderController(ProductServiceClient productServiceClient) {
        this.productServiceClient = productServiceClient;
    }

    @GetMapping("/orders/{productId}")
    public String createOrder(@PathVariable String productId) {
        Product product = productServiceClient.getProductById(productId);
        return "Order created for product: " + product.getName() + " with price: $" + product.getPrice();
    }
}

Explanation:

• @RestController: Marks this class as a REST controller.
• @GetMapping("/orders/{productId}"): Maps GET requests to /orders/{productId} to this method.
• ProductServiceClient productServiceClient: Injects the Feign client for communication with product-service.

Step 4: Run the Microservices

1. Start product-service: Run the ProductServiceApplication class.
2. Start order-service: Run the OrderServiceApplication class.

Step 5: Test the Communication

Open your browser or use a tool like Postman to test the endpoints:

• product-service: http://localhost:8081/products/1
• order-service: http://localhost:8082/orders/1

The response from order-service should include the product details fetched from product-service.

Conclusion

You have successfully set up two Spring Boot microservices and enabled communication between them using REST APIs and Feign clients. This setup allows you to build scalable and maintainable microservices architecture. This example can be expanded to include more microservices and more complex inter-service communication patterns.